One of New York's best collections of pinball is hidden in a secret bar in the back of this laundromat.

This upscale streetwear store is hidden behind a fake Snapple machine in the back of a deli.

This free, take-a-book shop seems like a trick but isn't.

Crammed into a Baltimore row house is an oddities shop that sells everything from skulls to dead insects.

A historic 1890s architectural masterpiece with an iconic clock tower that, once open to the public, now faces an uncertain future.

This shop for all your super spy needs hides an educational secret.

NYC's legendary underground network for bovine transportation.

One of the last few places in Manhattan that employed a pneumatic systemic keeps it on display.

Illegal drag racing two stories beneath Chicago’s streets.

Cretean quarry suggests real-life site for ancient Greek myth of the man-eating Minotaur in his labyrinth.

The world's only museum devoted to the wonders of fluorescence.

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

A 90-year-old underground water reservoir offers a more industrial kind of tranquility.

The hidden lair of an alchemist rediscovered in a 2002 flood.

The bluer than blue waters in these natural Israeli caves are reached via the world's steepest cable car.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

Hide from the tourist hordes in these relatively unknown, and unguarded lava caves.

A once-glowing grotto at the bottom of Waikapalae Wet Cave.

This luxury hotel suite is located deep in the bowels of an old mine.

A former top secret nuclear fallout shelter now operates like a hotel stuck in the Cold War.

The largest cave shaft in the world is home to thousands of birds and popular with BASE jumpers.

These tourist trap caverns are said to be the former home of a legendary Pennsylvania Hermit.

Inside this mountain lies several kilometers of breathtaking caves.